The present invention relates to a driving apparatus utilized for rotating position control, such as an electronic control throttle body or the like.
Conventionally, a torque motor is used as an actuator for an electronic throttle body for an internal combustion engine. With this kind of motor, it is possible to magnetize a rotor itself. However, generally, a ring-shaped magnet is stuck on a rotor so that the rotating position is controlled in accordance with the changes of magnetic flux distribution generated by a coil and magnetic path.
With a throttle body, the rotating range of a throttle valve to open and close an intake passage is about 90 degrees. Therefore, all of the ring-shaped magnet is not needed to drive and control within this range. Furthermore, the magnetic flux density of the magnet used for the rotor is high, resulting in high cost.
Consequently, as shown in FIG. 7, a torque motor with segment-type magnets was devised. In this figure, numeral 1 is a rotor, and two segment-type magnets 2, 2 cover about two thirds of the circumference of the rotor 1. A yoke 3 and a core 4 are disposed so that there is some air-gap about the circumference of the magnet 2. A coil 5 is disposed at the core 4. Numeral 6 is a default opening adjusting groove to set a stop position for the rotor when power is not applied.
With the abovementioned structure, when power is applied to the coil 5, the rotor 1 rotates about an axis O, and the throttle valve which is connected directly to the rotor 1 opens and closes. In this example, because magnets 2, 2 cover two thirds of the circumference of the rotor 1, its rotating angle is about 120 degrees. The rotating direction of the rotor 1 changes in accordance with the direction of the electric current which is passing through the coil 5.
With the abovementioned torque motor 10, the torque generated at the rotor 1 is not constant. As shown in FIG. 8, the torque is maximum at the center of the rotating position (the position where the boundary 2a between the two magnets 2, 2 overlaps with a center line a of the torque motor, in FIG. 7). The torque becomes small as it rotates from this position to the left or the right, and the torque is minimum at both ends of the rotating range. This is a characteristic of the torque motor 10 which has the abovementioned structure, caused by magnetic circuit, such as magnetizing angles of the magnets, magnetic saturation and so on.
When this torque motor 10 is used for opening and closing a throttle valve, as shown in FIG. 8, a full-closed position (an idling position) and a full-open position of the throttle valve are in the vicinity of each end of the operating range respectively. Namely, they correspond to positions with small torque.
Here, in the small opening range including the full-closed position, quick response is needed because this range is used frequently. Furthermore, in this range, excess torque is needed to overcome throttle valve sticking problems which can easily occur due to icing or deposits.
The present invention is devised in consideration of the abovementioned situation, and the object is to provide a driving apparatus with a non-circular gear which can output required torque at a specific rotating position, such as the small opening range of the throttle body.
To achieve the abovementioned object, the driving apparatus of the present invention comprises a torque motor as a driving source, and a gear train which transmits rotation of a motor shaft of the torque motor to a driven shaft, wherein the gear train comprises a non-circular driving gear which is attached to the motor shaft and a non-circular driven gear which is attached to the driven shaft and engaged with the non-circular driving gear.
Furthermore, a structure wherein either the non-circular driving gear or the non-circular driven gear is a sector type gear having an oval shape, or a structure wherein the non-circular driven gear is disposed at a throttle shaft which controls intake-air amount to an internal combustion engine can be adopted.
The torque motor can be a motor which has a rotating range less than 360 degrees and which changes the torque in accordance with the rotating angle.
With the driving apparatus of the present invention, when the torque motor rotates, the rotation is transmitted to the driven shaft via a gear train. The gear train includes the non-circular driving gear and the non-circular driven gear. Because of the engagement of these gears, the rotating velocity of the driven shaft is not constant, namely, rotating velocity of some ranges is high and that of other ranges is low. Here, the torque transmitted to the driven shaft in the high velocity range is smaller, and is larger in the low velocity range than the torque of the motor shaft. By designing the non-circular gear appropriately, it is possible to obtain desired torque at a desired rotating position, for example, to obtain increased torque when the driven gear is at the specific rotating position.